1. Field of the Invention
The present invention relates to information recording and reproducing techniques and, more particularly, to an information recording method and apparatus of a multi-value level type for recording information on a computer-readable recording medium, and to a computer-readable recording medium on which information is recorded by such a recording method.
2. Description of the Related Art
In recent years, a CD-R disc, a CD-RW disc, a DVD+R disc, a DVD+RW disc, etc., have become popular as a computer-readable information recording medium. Generally, when reproducing information recorded on such an information recording medium, a clock signal and a synchronization signal are acquired by detecting clock marks and synchronization marks recorded on the information recording medium.
Conventionally, with respect to the clock extraction and the synchronization signal, a bit stream is converted into bytes correctly, even if there is a bit-slip generated due to a defect on the bit stream, so as to prevent generation of excessive data error (For example, refer to Japanese Laid-Open Patent Application No. 7-320419).
Additionally, with respect to necessity of the clock marks in the case of multi-value recording, there are provided a multi-value data part in which multi-value information is recorded and a bit part in which synchronization bits are recorded to generate a demodulation clock for acquiring a timing for reproducing the multi-value information recording in the multi-value data part so as to generate said demodulation clock from an electric signal corresponding to said synchronization bits and detect a signal level of the electric signal corresponding to said multi-value information by being synchronized with the demodulation clock (for example, refer to Japanese Laid-Open Patent Application No. 4-219626 (Japanese Patent No. 2914732)).
When information is recorded on a recording medium at a multi-value level, since it is difficult to extract a clock from a reproduction signal, marks exclusive for extracting the clock on the recording medium are recorded on the recording medium. At the time of reproduction, since the interval of the clock marks fluctuates due to fluctuation in rotation of the recording medium, marks having a larger window width than the fluctuation are needed. Moreover, marks that do not generate erroneous synchronization are needed within the window width, and synchronization marks for recovering a bit-slip generated by a defect or the like are necessary synchronization marks. Since the fluctuation of the synchronization marks is larger than the clock marks, a larger window is needed.
Moreover, if a signal defect causing a bit-slip is generated actually, the phase of the clock shifts greatly and the reliability of the signal is spoiled greatly. Thus, in order to match the phase of the clock, in the conventional method, the phase is gradually matched using a plurality of clock marks. Therefore, there is a possibility of error occurring in reproduction data until phase synchronization is acquired even after the signal is recovered.
Moreover, in a case of binary recording, since the clock can be extracted from the reproduction signal, it is possible to pull-in the clock automatically when the reproduction signal is recovered even if the reproduction signal is temporarily missed. However, in the multi-value recording, there is a problem in that a time until the phase is pulled-in becomes long as mentioned above.